This invention relates to an integrated coal-fired gas turbine power plant and more particularly to an integrated power plant employing a hydraulic compressor-gas turbine combined cycle.
Integrated coal-fired gas turbine power plants are well-known. A typical integrated plant includes a coal combustion system wherein a gaseous effluent is produced, an expansion turbine driven by the gaseous effluent, and a compressor which provides pressurized air useful in the coal-combustion system. Additionally, plants of this type may include secondary cycles wherein the waste heat contained in the exhaust of the gas turbine is utilized in a heat recovery steam generator to produce steam for driving a cooperating steam turbine electrical generator assembly. A plant of the foregoing type is described by Woodmansee in U.S. Pat. No. 4,150,953, assigned to the assignee hereof.
The present invention provides an improvement over these conventional power plant designs through the use of a hydraulic compressor with its attendant performance advantages in an integrated power plant. In addition to an increase in performance, the employment of a hydraulic compressor as described herein allows the beneficial elimination of the secondary steam cycle and of the mechanical compressor typical of conventional integrated plants of this type.
Heretofore, hydraulic compressors have been used primarily in air supply systems for mining operations, however their use in integrated power plants can provide several important advantages over the use of a mechanical compressor in a similar system. In particular, hydraulic compressors operate isothermally, thereby requiring significantly less work input than would the isentropic process of a mechanical compressor. For example, in an ideal process isothermal compression typically requires only 70.7% of the work input necessary to achieve a similar level of compression in an isentropic process when operating at typical large gas turbine pressure ratios (e.g. 10). Furthermore, the efficiency of an actual mechanical compressor is approximately 84% versus the efficiencies of approximately 85% for the hydraulic compressor and approximately 92% for an associated hydraulic pump. This results in a 24% net energy savings for a gas turbine-driven hydraulic pump/hydraulic compressor system, (Wa.sub.h), as compared to a gas turbine-driven mechanical compressor system, (Wa.sub.m), as seen from the following: ##EQU1## Wa.sub.isothermal .perspectiveto.0.707Wa.sub.isentropic .thrfore.Wa.sub.h .perspectiveto.0.76Wa.sub.m
The isothermal process of the hydraulic compressor also provides a low temperature heat sink which can be used advantageously in conjunction with the waste heat contained in the exhaust of a gas turbine in an integrated power plant system. This waste heat is not normally added to the warm air (approx. 650.degree. F.) exiting a conventional compressor since this would result in an efficiently large amount of heat remaining in the system exhaust stream. For example, in such a system gas exhausted from the turbine at 1000.degree. F. might typically leave the system at 700.degree. F. Thus, integrated plants of this type have typically employed costly steam bottoming cycles to recover more of this gas turbine waste heat. Additionally, these bottoming cycles have required a supply of heat from the cooperating combustion system to operate properly, resulting in a decreased heat supply for the gas turbine.
The relatively cool (approx. 100.degree. F.) compressed air supplied by an isothermal hydraulic compressor allows for greater heat recapture from gas turbine exhaust resulting in system exhaust temperatures limited primarily by sulfuric acid formation in an associated regenerator at approx. 300.degree. F. Thus, the need for a steam bottoming cycle is obviated. Consequently, the capital cost elements of the steam cycle and its heat transfer components are eliminated. Similarly, the high maintenance costs associated with a steam turbine cycle, as well as those associated with a mechanical compressor, are avoided since the mechanically simple hydraulic compressor system involves few moving parts. Moreover, the elimination of the steam turbine bottoming cycle through the practice of the present invention allows all of the heat energy available in a particular coal combustion system to be supplied to the resultant gaseous effluent rather than to a steam turbine as in conventional designs. (See, for example, "Commercial Power Plant Design Development for the Coal-Fired Combined Cycle", ASME Publication 77-JPGC-GT-6, by J. R. Petersen and V. H. Lucke.)
Finally, the availability of relatively low temperature compressed air resulting from the isothermal compression process of a hydraulic compressor system can be useful as described herein to remove many of the operating constraints imposed on gas turbine operations by the presence of coal-related contaminants. These contaminants are borne by the gaseous effluent entering a turbine from the coal combustion system of an integrated power plant. In particular, alkali metals such as sodium and potassium go into their vapor phase at the temperature levels typically experienced in a coal combustion system. These alkali contaminants can subsequently condense on portions of the turbine causing the affected turbine parts to corrode, resulting in a corresponding decrease in turbine life.
It is recognized that the rate of alkali corrosion attack is strongly temperature dependent on the operating temperature range of a gas turbine, with the rate of corrosion decreasing with decreasing temperature. Thus, by making the relatively low temperature compressed air from a hydraulic compressor available for turbine cooling, the metal temperature of affected turbine parts can be lowered to thereby decrease the rate of corrosion thereof to within acceptable limits. Furthermore, the relatively clean low-temperature compressed air provided by a hydraulic compressor can also be diverted to gaseous effluent cleanup systems contained in most coal combustion systems to act as a dilutent or to enable the condensaton of contaminants within the cleanup system. The gas turbine operating conditions are thus improved, as is the overall performance of the associated integrated power plant, through the employment of a hydraulic compressor.
Accordingly, an object of the present invention is to provide a new and improved integrated coal-fired power plant with improved cycle efficiency and decreased system maintenance costs.
Another object of the present invention is to reduce the cost and complexity of conventional integrated coal-fired power plants.
Another object of the present invention is to provide a new and improved integrated coal-fired power plant with reduced coal-contaminant induced constraints.
Another object of the present invention is to provide a new and improved integrated coal-fired power plant employing a hydraulic compressor/gas turbine combined cycle.
Still another object of the present invention is to provide a new and improved method for the utilization of coal in an integrated gas turbine power plant.